Modern radio communications networks have strict requirements in terms of capacity, coverage and achievable bit rates. These requirements have to be met while ensuring that the battery lifetime of a user equipment served in the radio communications network is not quickly drained. One of the most relevant features that may affect a performance of capacity, coverage and achievable bit rates is power control. In radio communications networks the user equipments are communicating via a radio base station by transmitting data to the radio base station in an uplink (UL) transmission. The data is transmitted by the user equipment using a transmission power. Specifically, in case of the uplink where the battery life is more of a significant problem, power control of the transmission power plays an important role in balancing between a transmission power to obtain a desired signal to noise ratio of a signal at the radio base station, and an interference at a neighbouring radio base station in the radio communications network which the transmission power would simultaneously cause.
A power control scheme usually comprises a combination of an open loop component and a closed loop component. The open loop component is responsible of setting a rough operating point of transmission power whereas the closed loop component is responsible for fine tuning of the transmission power.
In Orthogonal Frequency Division Multiplexing (OFDM) based networks such as Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) networks, the transmissions within one cell are in general orthogonal along the frequency dimension. This means that the most dominant form of interference is inter-cell interference to or from neighbouring cells.
As mentioned above, the power control comprises two components: the closed loop component and the open loop component. The open loop component comprises mainly of two parameters, P0 and α. P0 is a base level component that represents a target power at the radio base station. The parameter α, known as the fractional pathloss compensation component, is used to control how much of the pathloss to its own cell a user equipment should compensate for by adjusting, i.e. increasing or decreasing, its own transmission power.
In short, the combination of P0 and α would allow the radio base station to configure a degree to which the user equipment responds to the pathloss where α is used parameter to trade off between the fairness of UL scheduling and an average cell throughput. Allowing full pathloss compensation, i.e. α=1 as α≦1, would allow transmissions from a user equipment located at a cell edge to be received with a higher power at the radio base station. However, when looking at a multi-cell system, a full pathloss compensation would lead to a significant increase in the inter-cell interference which would subsequently lead to a decrease in the average cell throughput and inherently decrease the performance of user equipments at the cell edge as these are the most vulnerable to inter-cell interference.
The general method of choosing α and P0 is based on system level simulations where a trade off between cell edge performance and average cell performance is obtained, which would result in a suitable value of α and/or P0 to be used for all user equipments in a cell. The agreed values to be used for fractional pathloss compensation component α are today 0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1, wherein 0 indicates no compensation for the pathloss and 1 indicates full compensation for the pathloss.
Current solutions try to find the optimal α and/or P0, similar α and P0 to all user equipments within a cell, or in the whole system, that are good compromises between cell throughput and cell coverage. However, these solutions have not resulted in optimal performance of the network.